The present invention relates generally to apparatus utilized to control fluid flow in a subterranean well and, more particularly provides a choke for selectively regulating fluid flow into or out of a tubing string disposed within a well.
Typically, a flow control apparatus is used to throttle or choke fluid flow into a production tubing string of a subterranean hydrocarbon well. Such flow control chokes are particularly useful where multiple zones are produced and it is desired to regulate the rate of fluid flow into the tubing string from each zone. Additionally, regulatory authorities may require that rates of production from each zone be reported, necessitating the use of a choke apparatus or other methods of determining and/or controlling the rate of production from each zone. Safety concerns may also dictate controlling the rate of production from each zone.
Flow chokes are also useful in single zone completions. For example, in a single wellbore producing from a single zone, an operator may determine that it is desirable to reduce the flow rate from the zone into the wellbore to limit damage to the well, reduce water coning and/or enhance ultimate recovery.
Downhole valves, such as sliding side doors, are designed for operation in a fully closed or fully open configuration and, thus, are not useful for variably regulating fluid flow therethrough. Downhole chokes typically are provided with a fixed orifice which cannot be variable without intervention. These are placed downhole to limit flow from a certain formation. Unfortunately, conventional downhole valves and chokes are also limited in their usefulness because intervention is required to change the fixed orifice or to open or close the valve. Additionally, it is difficult to open a sliding side door slowly against a large differential pressure (such as, in excess of 2500 psi) without damage to any of the door seals because these seals must pass through the flow.
What is needed is a flow control apparatus which is rugged, reliable, and long-lived, so that it may be utilized in completions without requiring frequent service, repair or replacement. To compensate for changing conditions, the apparatus should be adjustable. The apparatus should be resistant to erosion, even when it is configured between its fully open and closed positions, and should be capable of accurately regulating fluid flow. Additionally, there is a need for a variable choke which can open against a high differential pressure without excessive damage to the choke seals.
Such a downhole variable choking device would allow an operator to maximize reservoir production into the wellbore. It would be useful for completions, including any well where it is desired to control fluid flow, such as gas wells, oil wells, and water and chemical injection wells, in sum, in any downhole environment for controlling the flow of fluids.
This is accordingly an object of the present invention to provide such a flow control apparatus which permits infinitely variable downhole flow choking as well as the ability to shut off fluid flow, and associated methods of controlling fluid flow within a subterranean well.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, an annular choke apparatus, and methods of use, are provided for use within a subterranean well. In broad terms, a choke tool apparatus is provided which includes an outer housing having an outer housing wall with a least one flow port therethrough, and a variable annular flow-area choke disposed within the outer housing, the variable annular flow-area choke having a first generally tubular member sealingly disposed within the outer housing, the first tubular member having a shoulder with a sealing surface, a second generally tubular member slidingly and sealingly disposed within the outer housing, the second tubular member having a shoulder with a sealing surface, the second member movable between a sealed position wherein the sealing surfaces are in sealing abutment and an open position wherein the sealing surfaces are spaced apart. The sealing surfaces preferably provide a metal-to-metal seal. The variable annular flow-area choke described herein preferably provides for infinite adjustment between open and closed positions for precise flow regulation. The apparatus may include an actuator, locking, adjustment and biasing assemblies. In gas lift and other operations it may be desirable to variably regulate the flow without sealing the valve.
These and other aspects, features, objects, and advantages of the present invention will be more fully appreciated following careful consideration of the detailed description and accompanying drawings set forth hereinbelow.